A strange new kind of galactic beast has been spotted in the cosmic wilderness. Dubbed "super spirals," these unprecedented galaxies dwarf our own spiral galaxy, the Milky Way, and compete in size and brightness with the largest galaxies in the universe.
Super spirals have long hidden in plain sight by mimicking the
appearance of typical spiral galaxies. A new study using archived NASA
data reveals these seemingly nearby objects are in fact distant,
behemoth versions of everyday spirals. Rare, super spiral galaxies
present researchers with the major mystery of how such giants could have
arisen.
"We have found a previously unrecognized class of spiral galaxies
that are as luminous and massive as the biggest, brightest galaxies we
know of," said Patrick Ogle, an astrophysicist at the Infrared
Processing and Analysis Center (IPAC) at the California Institute of
Technology in Pasadena and lead author of a new paper on the findings
published in The Astrophysical Journal. "It's as if we have just
discovered a new land animal stomping around that is the size of an
elephant but had shockingly gone unnoticed by zoologists."
Ogle and colleagues chanced upon super spirals as they searched for
extremely luminous, massive galaxies in the NASA/IPAC Extragalactic
Database (NED), an online repository containing information on over 100
million galaxies. NED brings together a wealth of data from many
different projects, including ultraviolet light observations from the
Galaxy Evolution Explorer, visible light from Sloan Digital Sky Survey,
infrared light from the Two Micron All-Sky Survey, and links to data
from other missions such as Spitzer and the Wide-?eld Infrared Survey
Explorer, or WISE.
"Remarkably, the finding of super spiral galaxies came out of purely
analyzing the contents of the NASA/IPAC Extragalactic Database, thus
reaping the benefits of the careful, systematic merging of data from
many sources on the same galaxies," said George Helou, a study co-author
and the executive director of IPAC. "NED is surely holding many more
such nuggets of information, and it is up to us scientists to ask the
right questions to bring them out."
Ogle, Helou and their colleagues expected that humongous, mature
galaxies called ellipticals -- so named for their football-like shapes
-- would dominate their search within NED for the most luminous
galaxies. But a tremendous surprise lay in store for the scientists.
In a sample of approximately 800,000 galaxies no more than 3.5
billion light-years from Earth, 53 of the brightest galaxies
intriguingly had a spiral, rather than elliptical, shape. The
researchers double-checked the distances to the spiral galaxies and saw
that none were nearby -- even the closest lay some 1.2 billion
light-years away. With the correct distance estimates in hand, the
stunning properties of this newfound batch of whirlpool-shaped galaxies
came to light.
Super spirals can shine with anywhere from eight to 14 times the
brightness of the Milky Way. They possess as much as 10 times our
galaxy's mass. Their gleaming, starry disks stretch from twice to even
four times the width of the Milky Way galaxy's approximately 100,000
light-year-wide disk, with the largest super spiral spanning a whopping
440,000 light-years. Super spirals also give off copious ultraviolet and
mid-infrared light, signifying a breakneck pace of churning out new
stars. Their star formation rate is as high as 30 times that of our own
run-of-the-mill galaxy.
According to established astrophysical theory, spiral galaxies should
not be able to attain any of these feats because their size and
star-making potential are limited. As spiral galaxies grow by
gravitationally attracting fresh, cool gas from intergalactic space,
their masses reach a tipping point in which any newly captured gas
rushes in too rapidly. This headlong gas heats up and prevents
subsequent star formation in a process known as "quenching." Bucking
this conventional wisdom, though, super spirals remain unquenched.
A vital hint about the potential origin of super spirals is that four
out of the 53 seen by Ogle and colleagues clearly contain two galactic
nuclei, instead of just one as usual. Double nuclei, which look like two
egg yolks frying in a pan, are a telltale sign of two galaxies having
just merged together. Conventionally, mergers of spiral galaxies are
destined to become bloated, elliptical galaxies. Yet Ogle and colleagues
speculate that a special merger involving two, gas-rich spiral galaxies
could see their pooled gases settle down into a new, larger stellar
disk -- presto, a super spiral.
"Super spirals could fundamentally change our understanding of the
formation and evolution of the most massive galaxies," said Ogle. "We
have much to learn from these newly identified, galactic leviathans."
Other authors of the new study are Lauranne Lanz of IPAC and Cyril
Nader, an undergraduate student at the University of California, Los
Angeles, who worked on this project during a summer internship at IPAC.
NASA's Jet Propulsion Laboratory, Pasadena, California, manages the
Spitzer Space Telescope mission for NASA's Science Mission Directorate,
Washington. Science operations are conducted at the Spitzer Science
Center at the California Institute of Technology in Pasadena. Spacecraft
operations are based at Lockheed Martin Space Systems Company,
Littleton, Colorado. Data are archived at IPAC. Caltech manages JPL for
NASA.
For more information about Spitzer, visit: http://spitzer.caltech.edu
Media Contact :
Written by Adam Hadhazy
Whitney Clavin
Jet Propulsion Laboratory, Pasadena, California
818-354-4673
whitney.clavin@jpl.nasa.gov
Source: JPL-Caltech
